1. Field of the Invention
The present invention relates to a rear projector having an image generator including an electric optical device for modulating a light beam irradiated by a light source to form an optical image in accordance with image information and a projection optical system for enlarging and projecting the optical image, a casing for disposing the image generator, and a screen exposed on one of the lateral sides of the casing onto which the optical image formed by the image generator is projected
2. Description of Related Art
Recently, a rear projector has come to be used in the field of home theater etc. Such rear projector has an image generator for generating a projection image, a box-shaped casing disposing the image generator and a reflection mirror for reflecting the projected image and a transmissive screen exposed to a side of the box-shaped casing.
The image generator has a light source lamp, an optical device such as a liquid crystal panel for modulating a light beam irradiated by the light source lamp in accordance with image information, and a projection optical system such as a projection lens for enlarging and projecting the generated optical image.
The optical image formed by the image generator is projected on a transmissive screen after being reflected by a mirror etc., so that the image transmitted through the screen is viewed.
Such rear projector also accommodates acoustic device such as a speaker inside the casing thereof, so that the large-screen image has much presence with the use of the acoustic device.
Incidentally, the image generator of such rear projector has the light source lamp, a light source driving block for driving the light source lamp, and a power source block for supplying electric power to the board for controlling the drive of the optical device, all of which are heat source. On the other hand, some of the components of the optical device etc. are weak against heat. Accordingly, it is important to cool the interior of the projector efficiently.
In a conventional arrangement, an intake opening and an exhaust opening are provided on a front side of a casing of a rear projector, i.e. on the side provided with a screen, through which the cooling air is introduced into/discharged from the projector.
However, when the external air is used to cool the electric optical device, dust etc. flowing outside may sometimes be sucked in together with the air. When the dust etc. is adhered on an image formation area of the electric optical device, the dust is displayed as shadow on the screen, thereby deteriorating the quality of the image displayed on the screen.
It is possible to provide a filter etc. on the intake opening to prevent dust from being sucked in, improvement in cooling efficiency by increasing the amount of the sucked air often hinders improvement in dust proofness, so that it is difficult to securely prevent the dust while improving the cooling efficiency.
An object of the present invention is to provide a rear projector capable of securely avoiding invasion of dust while improving cooling efficiency.
A rear projector according to an aspect of the present invention comprises: an image generator having an electric optical device that modulates the light beam irradiated by a light source to form an optical image in accordance with image information and a projection optical system that enlarges and projects the optical image; a casing that disposes the image generator; and a screen exposed on one of the sides of the casing onto which the that disposes the image generator and a second casing provided with the screen, the electric optical device being located in a closed space including a space inside the second casing, where a circulation fan that circulates an air inside the closed space is provided in the closed space.
Though the electric optical device is cooled by circulating the air inside the closed space, the other component such as the light source lamp and the power source block may preferably be cooled by drawing outside air from the intake opening as in the conventional arrangement. This is because adhesion of slight dust to the components scarcely influences on the image quality unlike the electric optical device.
According to the present invention, since the electric optical device can be cooled by circulating the air inside the closed space by the circulation fan, invasion of dust from the outside can be prevented while efficiently cooling the electric optical device.
Further, since the large screen of forty to sixty inches is provided on the second casing and vast space can be secured inside the second casing, the electric optical device can be sufficiently cooled by the vast space.
In the above arrangement, the circulation fan may preferably be located opposite to the second casing relative to the electric optical device.
According to the above arrangement, since the electric optical device can be cooled by the air discharged by the circulation fan and the air having cooled the electric optical device is discharged to and circulated in the space inside the second casing, the electric optical device can be cooled by the entire air inside the closed space, thereby enhancing cooling efficiency.
In the above arrangement, a radiator that radiates the heat inside the second casing to cool the air may preferably be provided on the second casing.
The radiator may preferably have a heat receiver provided inside the second casing and a plurality of cooling fins connected with the heat receiver and projected to the outside of the second casing, which may be a heat sink having integrated heat receiver and cooling fin. Alternatively, the heat receiver and cooling fin may be separately formed and a Peltier element is used as the heat receiver, thus forcibly radiates the heat inside the second casing toward outside.
According to the above arrangement, since the heat of the air heated after cooling the electric optical device is radiated to the outside of the casing, the cooling efficiency can be enhanced.
Since the heat sink integrating the heat receiver and the cooling fin is used as the radiator, the construction can be simplified and the number of the component can be reduced.
On the other hand, when a Pertier element is used as the heat receiver, heat migration from the inside of the casing to the outside can be controlled, thereby further enhancing cooling efficiency.
In the above arrangement, a duct that guides the air discharged by the circulation fan along the inner circumference of the casing may preferably be provided inside the second casing. At this time, the duct may preferably cover the electric optical device.
According to the above arrangement, since the air convection inside the second casing can be controlled by the duct, the electric optical device can be cooled using the entire air inside the second casing.
Further, since the duct covers the electric optical device, the light leaked from the electric optical device can be blocked, thereby preventing deterioration of contrast of the projected image caused when the leaked light is projected on the screen.
The circulation fan may preferably be a sirocco fan that discharges the air drawn in rotation axis direction to rotary tangential line direction.
According to the above arrangement, since the discharge pressure of air can be increased, the air inside the large closed space including the interior of the second casing can be securely circulated. This is because the sirocco fan has relatively small opening area on the discharge side as compared to the opening area of the air-drawing side thereof and because the discharge pressure can be increased by discharging the air in a rotary tangential direction.